3T3-L1 cells were treated with methylisobutylxanthine, dexamethasone, and insulin to induce fatty metamorphosis. Incubation of differentiated 3T3-L1 cells with 1 MuM epinephrine results in 3- to 4-fold increase in cellular cAMP within 2-4 min with rapid decline thereafter. Pretreatment with 100 pM insulin for 8 min decreases the peak concentration of cAMP while incubation with 10 nM dexamethasone for 72 hr maintains the elevated cellular cAMP for 20-30 min and delays the decline in cAMP. We have previously shown that incubation with 100 pM insulin or 1 MuM epinephrine increases particulate cAMP phosphodiesterase activity by about 40-60% within 8 min and that 10 nM dexamethasone for 72 hr can block this effect. Incubation of undifferentiated or differentiated 3T3-L1 cells with 1 MuM dexamethasone results in 50% suppression of soluble calmodulin-sensitive cGMP phosphodiesterase within 48 hr. Soluble cAMP phosphodiesterase was suppressed by 20-30% by this treatment. Higher concentrations of dexamethasone (1 MuM) for 72 hr could suppress particulate cAMP and cGMP phosphodiesterase activities by 20-30%. Column chroamtography on DEAE-biogel of soluble fractions revealed similar elution profiles for basal and calmodulin-sensitive cGMP phosphodiesterase in control and dexamethasone-treated cells but less activity in eluates from the dexamethasone-treated cells. Calmodulin-Sepharose chromatography of crude soluble fractions confirmed a 50% decrease in calmodulin-sensitive cGMP phosphodiesterase after treatment with 10 nM dexamethasone for 72 hr.